Recently, there has been an explosive increase in the demand for portable electric and electronic apparatuses. As a result, rechargeable batteries are also increasingly in demand. Particularly, rechargeable lithium batteries are those of primary interest. Additionally, as portable electric and electronic apparatuses become smaller and more multi-functionalized, it is required that batteries used therein have a high performance, a compact size and various shapes. More particularly, in a notebook PC, the size of a battery greatly affects the thickness of a notebook PC. Therefore, many attempts have been made in order to reduce the thickness of a battery as well as to provide a battery having a high capacity and a high performance. Further, since environmental problems have been raised as some of the most serious problems in the world, solutions for the global warming phenomenon have been discussed sincerely and continuously.
As a solution for such environmental problems, a bill has been discussed in many countries to reduce the use of fossil fuels for automobiles, which is a primary cause for global warming, and to enforce obligatory use of environmental-friendly electric cars. A part of the bill will become effective hereafter. Additionally, in order to solve some environmental pollution problems, research and development into electric cars (HEV, EV) are continuously being made, and some kinds of electric cars have come into general usage. Therefore, a battery having a high capacity and excellent high-rate discharge property is in demand, and a novel approach to improve the thermal stability of such a battery is also in demand. In order to satisfy such demands, there has been an attempt to increase the width and the height of batteries for use in cars.
In general, a rechargeable lithium battery comprises an electrode assembly composed of a positive electrode comprising lithium cobalt oxide active materials, a negative electrode comprising carbon-based active materials and a separator; and an aluminum-laminated film for enclosing the electrode assembly. The structure of such a rechargeable lithium battery is shown in FIG. 1, wherein the electrode assembly has a stacked configuration as shown in FIG. 2. Particularly, the positive electrode is made by coating the positive electrode active materials on an aluminum foil, and the negative electrode is made by coating the negative electrode active materials on a copper foil. Due to the structural characteristic of batteries, a battery having a large surface area has advantages in that it permits an increased capacity and a simplified battery shape. However, when the electrodes and the separator are simply stacked, in the case of an electrode having a large surface area, it is difficult to obtain close and uniform contact between each electrode and the separator. Also, it is difficult to wet the whole surface area of the electrode with an electrolyte and to perform homogeneous electrode reactions over the whole surface area of the electrode during charge/discharge cycles. Accordingly, it is very difficult to obtain uniform battery performance. In other words, even if the electrode is apparently in a good state, the electrolyte contained therein may be in a depletion state locally, thereby causing rapid deterioration of the electrode and reducing the life of the battery. Further, when such a non-uniform state of the electrode becomes serious, the electrode reactions may occur only locally, and thus there is a possibility for local precipitation of lithium metal that is responsible for the deterioration of safety.
Meanwhile, it is known in the prior art that lamination using a gel polymer can improve the close contact between an electrode and a separator. However, in this case, some features of the battery including rapid impregnation of an electrode with an electrolyte, uniform wetting of an electrode with an electrolyte and a high-rate discharge property may be deteriorated.